The Prime Minister said both saving money and going green are important. However, people will not be persuaded to back green policies if ministers just talk about saving the planet.

Speaking on the Eastleigh by-election campaign trail, he said it was important to stress that saving energy and reducing reliance on fossil fuels are actually cost effective.

"In tough times, its important to explain to people that going green is not just about saving the planet it's about saving households money," he said.

"If we preach at people about greenery and make it all sound terribly expensive, I don't think we're going to take people with us."

Subsidies for low-carbon power, including nuclear and wind farms, will be added to bills over the next few decades, raising the cost of energy. However, the Government insists that green policies will keep bills down relative to what they would be if Britain continues to get its power from increasingly expensive fossil fuels.